Structure and photoisomerization of the Z-type Langmuir-Blodgett films of a new series of azo-containing chiral copolymers

Three copolymers, A1, A2, and A3, poly{2-hydroxyethyl methacrylate} _1-x-co-{6-[4-((((((S)-2-methylbutyl)-oxy)carbonyl)phenyl)azo)phenoxy] hexyl methacrylate}_x with x = 0.25, 0.50, and 0.75, respectively, were successfully deposited as Z-type Langmuir-Blodgett (LB) films. The isobar curves and the compression-expansion isotherms of the three copolymers on water show that the polymer monolayers have good quality. Polarized UV-vis and IR spectroscopic measurements reveal that the LB films of A1, A2, and A3 on substrates are organized with the long axis of azobenzene moiety preferentially along the film normal, and the LB films of A1 have additional in-plane orientation. The LB films of A1, A2, and A3 are all capable of trans-to-cis and cis-to-trans photoisomerizations. Photoinduced liquid crystal alignment alteration from the homeotropic mode to planar mode is achieved with the Z-type films of A1. It is concluded that the LB films of A1 have the right occupied molecular area for photoinduced liquid crystal alignment regulation.